Terminal apparatus and buffer partitioning method

ABSTRACT

Provided is a terminal device with which deterioration in hybrid automatic repeat request (HARQ) retransmission performance can be inhibited by continuing a downlink (DL) HARQ process for DL data before and after changing the uplink link-DL configuration. In this device, a decoder stores, in a retransmission buffer, DL data transmitted from a base station, and decodes the DL data, and a wireless transmitter transmits a response signal generated using a DL-data-error detection result. A soft buffer is partitioned into a plurality of regions for each retransmission process on the basis of the highest values among retransmission process numbers respectively stated in a plurality of configuration patterns which can be set in the terminal.

BACKGROUND Technical Field

The present invention relates to a terminal apparatus and a bufferdividing method.

Description of the Related Art

3GPP LTE employs Orthogonal Frequency Division Multiple Access (OFDMA)as a downlink communication scheme. In radio communication systems towhich 3GPP LTE is applied, base stations transmit synchronizationsignals (i.e., Synchronization Channel: SCH) and broadcast signals(i.e., Broadcast Channel: BCH) using predetermined communicationresources. Meanwhile, each terminal finds an SCH first and therebyensures synchronization with the base station. Subsequently, theterminal reads BCH information to acquire base station-specificparameters (e.g., frequency bandwidth) (see, Non-Patent Literature(hereinafter, abbreviated as NPL) 1, 2 and 3).

In addition, upon completion of the acquisition of the basestation-specific parameters, each terminal sends a connection request tothe base station to thereby establish a communication link with the basestation. The base station transmits control information via PhysicalDownlink Control CHannel (PDCCH) as appropriate to the terminal withwhich a communication link has been established via a downlink controlchannel or the like.

The terminal performs “blind-determination” on each of a plurality ofpieces of control information included in the received PDCCH signal(i.e., Downlink (DL) Assignment Control Information: also referred to asDownlink Control Information (DCI)). To put it more specifically, eachpiece of the control information includes a Cyclic Redundancy Check(CRC) part and the base station masks this CRC part using the terminalID of the transmission target terminal. Accordingly, until the terminaldemasks the CRC part of the received piece of control information withits own terminal ID, the terminal cannot determine whether or not thepiece of control information is intended for the terminal. In thisblind-determination, if the result of demasking the CRC part indicatesthat the CRC operation is OK, the piece of control information isdetermined as being intended for the terminal.

Moreover, in 3GPP LTE, Automatic Repeat Request (ARQ) is applied todownlink data to terminals from a base station. To put it morespecifically, each terminal feeds back a response signal indicating theresult of error detection on the downlink data to the base station. Eachterminal performs a CRC on the downlink data and feeds backAcknowledgment (ACK) when CRC=OK (no error) or Negative Acknowledgment(NACK) when CRC=Not OK (error) to the base station as a response signal.An uplink control channel such as Physical Uplink Control Channel(PUCCH) is used to feed back the response signals (i.e., ACK/NACKsignals (hereinafter, may be referred to as “A/N,” simply)).

The control information to be transmitted from a base station hereinincludes resource assignment information including information onresources assigned to the terminal by the base station. As describedabove, PDCCH is used to transmit this control information. This PDCCHincludes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCHconsists of one or more Control Channel Elements (CCE). To put it morespecifically, a CCE is the basic unit used to map the controlinformation to PDCCH. Moreover, when a single L1/L2 CCH consists of aplurality of CCEs (2, 4 or 8), a plurality of contiguous CCEs startingfrom a CCE having an even index are assigned to the L1/L2 CCH. The basestation assigns the L1/L2 CCH to the resource assignment target terminalin accordance with the number of CCEs required for indicating thecontrol information to the resource assignment target terminal. The basestation maps the control information to physical resources correspondingto the CCEs of the L1/L2 CCH and transmits the mapped controlinformation.

In addition, CCEs are associated with component resources of PUCCH(hereinafter, may be referred to as “PUCCH resource”) in a one-to-onecorrespondence. Accordingly, a terminal that has received an L1/L2 CCHidentifies the component resources of PUCCH that correspond to the CCEsforming the L1/L2 CCH and transmits a response signal to the basestation using the identified resources. However, when the L1/L2 CCHoccupies a plurality of contiguous CCEs, the terminal transmits theresponse signal to the base station using a PUCCH component resourcecorresponding to a CCE having a smallest index among the plurality ofPUCCH component resources respectively corresponding to the plurality ofCCEs (i.e., PUCCH component resource associated with a CCE having aneven numbered CCE index). In this manner, the downlink communicationresources are efficiently used.

As illustrated in FIG. 1, a plurality of response signals transmittedfrom a plurality of terminals are spread using a Zero Auto-correlation(ZAC) sequence having the characteristic of zero autocorrelation intime-domain, a Walsh sequence and a discrete Fourier transform (DFT)sequence, and are code-multiplexed in a PUCCH. In FIG. 1, (W₀, W₁, W₂,W₃) represent a length-4 Walsh sequence and (F₀, F₁, F₂) represent alength-3 DFT sequence. As illustrated in FIG. 1, ACK or NACK responsesignals are primary-spread over frequency components corresponding to 1SC-FDMA symbol by a ZAC sequence (length-12) in frequency-domain. To putit more specifically, the length-12 ZAC sequence is multiplied by aresponse signal component represented by a complex number. Subsequently,the ZAC sequence serving as the response signals and reference signalsafter the primary-spread is secondary-spread in association with each ofa Walsh sequence (length-4: W₀-W₃ (may be referred to as Walsh CodeSequence)) and a DFT sequence (length-3: F₀-F₂). To put it morespecifically, each component of the signals of length-12 (i.e., responsesignals after primary-spread or ZAC sequence serving as referencesignals (i.e., Reference Signal Sequence) is multiplied by eachcomponent of an orthogonal code sequence (i.e., orthogonal sequence:Walsh sequence or DFT sequence). Moreover, the secondary-spread signalsare transformed into signals of length-12 in the time-domain by inversefast Fourier transform (IFFT). A CP is added to each signal obtained byIFFT processing, and the signals of one slot consisting of seven SC-FDMAsymbols are thus formed.

The response signals from different terminals are spread using ZACsequences each corresponding to a different cyclic shift value (i.e.,index) or orthogonal code sequences each corresponding to a differentsequence number (i.e., orthogonal cover index (OC index)). An orthogonalcode sequence is a combination of a Walsh sequence and a DFT sequence.In addition, an orthogonal code sequence is referred to as a block-wisespreading code in some cases. Thus, base stations can demultiplex thecode-multiplexed plurality of response signals using the related artdespreading and correlation processing (see, NPL 4).

However, it is not necessarily true that each terminal succeeds inreceiving downlink assignment control signals because the terminalperforms blind-determination in each subframe to find downlinkassignment control signals intended for the terminal. When the terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminal wouldnot even know whether or not there is downlink data intended for theterminal on the downlink component carrier. Accordingly, when a terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminalgenerates no response signals for the downlink data on the downlinkcomponent carrier. This error case is defined as discontinuoustransmission of ACK/NACK signals (DTX of response signals) in the sensethat the terminal transmits no response signals.

In 3GPP LTE systems (may be referred to as “LTE system,” hereinafter),base stations assign resources to uplink data and downlink data,independently. For this reason, in the 3GPP LTE system, terminals (i.e.,terminals compliant with LTE system (hereinafter, referred to as “LTEterminal”)) encounter a situation where the terminals need to transmituplink data and response signals for downlink data simultaneously in theuplink. In this situation, the response signals and uplink data from theterminals are transmitted using time-division multiplexing (TDM). Asdescribed above, the single carrier properties of transmission waveformsof the terminals are maintained by the simultaneous transmission ofresponse signals and uplink data using TDM.

In addition, as illustrated in FIG. 2, the response signals (i.e.,“A/N”) transmitted from each terminal partially occupy the resourcesassigned to uplink data (i.e., Physical Uplink Shared CHannel (PUSCH)resources) (i.e., response signals occupy some SC-FDMA symbols adjacentto SC-FDMA symbols to which reference signals (RS) are mapped) and arethereby transmitted to a base station in time-division multiplexing(TDM). However, “subcarriers” in the vertical axis in FIG. 2 are alsotermed as “virtual subcarriers” or “time contiguous signals,” and “timecontiguous signals” that are collectively inputted to a discrete Fouriertransform (DFT) circuit in a SC-FDMA transmitter are represented as“subcarriers” for convenience. To put it more specifically, optionaldata of the uplink data is punctured due to the response signals in thePUSCH resources. Accordingly, the quality of uplink data (e.g., codinggain) is significantly reduced due to the punctured bits of the codeduplink data. For this reason, base stations instruct the terminals touse a very low coding rate and/or to use very large transmission powerso as to compensate for the reduced quality of the uplink data due tothe puncturing.

Meanwhile, the standardization of 3GPP LTE-Advanced for realizing fastercommunication than 3GPP LTE is in progress. 3GPP LTE-Advanced systems(may be referred to as “LTE-A system,” hereinafter) follow LTE systems.3GPP LTE-Advanced will introduce base stations and terminals capable ofcommunicating with each other using a wideband frequency of 40 MHz orgreater to realize a downlink transmission rate of up to 1 Gbps orabove.

In the LTE-A system, in order to simultaneously achieve backwardcompatibility with the LTE system and ultra-high-speed communicationseveral times faster than transmission rates in the LTE system, theLTE-A system band is divided into “component carriers” of 20 MHz orbelow, which is the bandwidth supported by the LTE system. In otherwords, the “component carrier” is defined herein as a band having amaximum width of 20 MHz and as the basic unit of communication band. Inthe Frequency Division Duplex (FDD) system, moreover, “componentcarrier” in downlink (hereinafter, referred to as “downlink componentcarrier”) is defined as a band obtained by dividing a band according todownlink frequency bandwidth information in a BCH broadcasted from abase station or as a band defined by a distribution width when adownlink control channel (PDCCH) is distributed in the frequency domain.In addition, “component carrier” in uplink (hereinafter, referred to as“uplink component carrier”) may be defined as a band obtained bydividing a band according to uplink frequency band information in a BCHbroadcasted from a base station or as the basic unit of a communicationband of 20 MHz or below including a Physical Uplink Shared CHannel(PUSCH) in the vicinity of the center of the bandwidth and PUCCHs forLTE on both ends of the band. In addition, the term “component carrier”may be also referred to as “cell” in English in 3GPP LTE-Advanced.Furthermore, “component carrier” may also be abbreviated as CC(s).

In the Time Division Duplex (TDD) system, a downlink component carrierand an uplink component carrier have the same frequency band, anddownlink communication and uplink communication are realized byswitching between the downlink and uplink on a time division basis. Forthis reason, in the case of the TDD system, the downlink componentcarrier can also be expressed as “downlink communication timing in acomponent carrier.” The uplink component carrier can also be expressedas “uplink communication timing in a component carrier.” The downlinkcomponent carrier and the uplink component carrier are switched based ona UL-DL configuration as shown in FIG. 3. The UL-DL configuration isindicated to a terminal by a broadcast signal called System InformationBlock Type 1 (SIB1) and the value thereof is the same throughout theentire system and it is assumed that the value is not frequentlychanged. In the UL-DL configuration shown in FIG. 3, timings areconfigured in subframe units (that is, 1 msec units) for downlinkcommunication (DL) and uplink communication (UL) per frame (10 msec).The UL-DL configuration can construct a communication system capable offlexibly meeting a downlink communication throughput requirement and anuplink communication throughput requirement by changing a subframe ratiobetween downlink communication and uplink communication. For example,FIG. 3 illustrates UL-DL configurations (Config 0 to 6) having differentsubframe ratios between downlink communication and uplink communication.In addition, in FIG. 3, a downlink communication subframe is representedby “D,” an uplink communication subframe is represented by “U” and aspecial subframe is represented by “S.” Here, the special subframe is asubframe at the time of switchover from a downlink communicationsubframe to an uplink communication subframe. In the special subframe,downlink data communication may be performed as in the case of thedownlink communication subframe. In each UL-DL configuration shown inFIG. 3, subframes (20 subframes) corresponding to 2 frames are expressedin two stages: subframes (“D” and “S” in the upper row) used fordownlink communication and subframes (“U” in the lower row) used foruplink communication. Furthermore, as shown in FIG. 3, an errordetection result corresponding to downlink data (ACK/NACK) is indicatedin the fourth uplink communication subframe or an uplink communicationsubframe after the fourth subframe after the subframe to which thedownlink data is assigned.

In the LTE-A system, studies are being carried out on a possibility ofchanging UL-DL configurations (hereinafter may be referred to as “TDDeIMTA (enhancement for DL-UL Interference Management and TrafficAdaptation).” Examples of objects of TDD eIMTA include provision of aservice that meets the needs of users by a flexible change of a UL/DLratio, a reduction of power consumption in a base station by increasinga UL ratio in a time zone with a low traffic load or the like. As amethod of changing a UL-DL configuration, studies are being carried outon (1) a method by indicating an SI (System Information) signaling base,(2) a method by indicating an RRC (higher layer) signaling base and (3)a method by indicating an L1 (Physical Layer) signaling base.

Method (1) corresponds to a change of a UL-DL configuration with thelowest frequency. Method (1) is suitable for cases where an objective isto reduce power consumption in a base station by increasing a UL ratio,for example, in a time zone with a low traffic load (e.g., midnight orearly morning). Method (3) corresponds to a change of a UL-DLconfiguration with the highest frequency. A small cell such as a picocell has fewer terminals to be connected than a large cell such as amacro cell. In a pico cell, UL/DL traffic of the entire pico cell isdetermined depending on the amount of UL/DL traffic in a small number ofterminals connected to the pico cell. For this reason, a violent timefluctuation in UL/DL traffic occurs in the pico cell. Therefore, method(3) is suitable for a case where a UL-DL configuration is changed inaccordance with a time fluctuation in UL/DL traffic in a small cell likea pico cell. Method (2) may be positioned between method (1) and method(3) and is suitable for a case where a UL-DL configuration is changedwith a medium degree of frequency.

The LTE system and LTE-A system support HARQ (Hybrid Automatic RepeatreQuest) (hereinafter, referred to as “DL HARQ”) of downlink data. In DLHARQ, the LTE terminal and LTE-A terminal store an LLR (Log LikelihoodRatio) (or may also be called “soft bit”) for downlink data in which anerror is detected in a soft buffer. The LLR stored in the soft buffer iscombined with an LLR corresponding to downlink data to be retransmitted(retransmission data). As shown in FIG. 4 and following equation 1, thesoft buffer (buffer capacity: N_(soft)) is divided into equal portionsbased on the number of downlink component carriers (K_(C)) supported bya terminal, the number of multiplexed layers (K_(MIMO)) supported by theterminal, and the maximum number of DL HARQ processes (M_(DL_HARQ))defined in the UL-DL configuration set in the terminal, and an IR(Incremental Redundancy) buffer size (N_(IR)) per transport block (orTB) is calculated. The maximum number of DL HARQ processes representsthe number of retransmission processes (the number of DL HARQ processes)set based on a maximum value of a retransmission interval (may also becalled “RTT (Round Trip Time)”) after transmission of downlink data inDL HARQ in each UL-DL configuration (Config#0 to #6) untilretransmission of the downlink data (see FIG. 5).

$\begin{matrix}{( {{Equation}\mspace{14mu} 1} )\mspace{616mu}} & \; \\{N_{IR} = \lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min ( {M_{{DL}\; \_ \; {HARQ}},M_{limit}} )}} \rfloor} & \lbrack 1\rbrack\end{matrix}$

As shown in FIG. 5, values of the maximum number of DL HARQ processesvary from one UL-DL configuration to another.

The terminal stores the LLR corresponding to the downlink data in whichan error has been detected in an IR buffer corresponding to each DL HARQprocess within a range of IR buffer size per TB calculated according toequation 1. Here, M_(limit) shown in equation 1 is an allowable value ofthe number of DL HARQ processes that can be supported by the terminal,stored in the soft buffer and the value of M_(limit) is, for example, 8.To reduce the total capacity of the soft buffer (soft buffer capacity),the IR buffer per TB cannot always store all systematic bits (LLR) perTB and all parity bits (LLR). Therefore, increasing the IR buffer sizeper TB as much as possible within the soft buffer capacity leads to anincrease in the total amount of LLR that can be stored in the IR bufferand consequently leads to an improvement of HARQ retransmissionperformance.

CITATION LIST Non-Patent Literature

NPL 1

-   -   3GPP TS 36.211 V10.1.0, “Physical Channels and Modulation        (Release 10),” March 2011

NPL 2

-   -   3GPP TS 36.212 V10.1.0, “Multiplexing and channel coding        (Release 10),” March 2011

NPL 3

-   -   3GPP TS 36.213 V10.1.0, “Physical layer procedures (Release        10),” March 2011

NPL 4

-   -   Seigo Nakao, Tomofumi Takata, Daichi Imamura, and Katsuhiko        Hiramatsu, “Performance enhancement of E-UTRA uplink control        channel in fast fading environments,” Proceeding of IEEE VTC        2009 spring, April. 2009

BRIEF SUMMARY Technical Problem

When different UL-DL configurations are set between terminals supportingTDD eIMTA, interference from uplink communication to downlinkcommunication (hereinafter may be referred to as “UL-DL interference”)may occur between the terminals. To avoid the occurrence of this UL-DLinterference, terminals supporting TDD eIMTA may change the UL-DLconfiguration not for each terminal (UE specific) but for each cell(cell specific).

When the UL-DL configuration is changed for each cell, many terminalssupporting TDD eIMTA are likely to change the UL-DL configuration whileall DL HARQ processes have not been completed (that is, no ACK has beenreturned to the base station).

Furthermore, as shown in FIG. 5, the maximum number of DL HARQ processes(M_(DL_HARQ)) varies among different UL-DL configurations. For thisreason, when the maximum number of DL HARQ processes corresponding toany one UL-DL configuration at least before and after the change is lessthan 8, the IR buffer size per TB also varies before and after thechange of the UL-DL configuration.

For example, as shown in FIG. 6, when Config#0 is changed to Config#1,the maximum number of DL HARQ processes is changed from 4 to 7. In thiscase, as shown in FIG. 6, since the number of divisions of the softbuffer also varies before and after the change of the UL-DLconfiguration, data reference positions in the soft buffer vary beforeand after the change of the UL-DL configuration. For this reason, theterminal cannot correctly read the stored data and cannot continue DLHARQ processes before and after the change of the UL-DL configuration.That is, there is concern about deterioration of HARQ retransmissionperformance before and after the change of the UL-DL configuration.Although the deterioration of HARQ retransmission performance isobserved in aforementioned method (1) of changing the UL-DLconfiguration or in the case of a change of the UL-DL configuration witha low or medium frequency as shown in method (2), such deterioration ofHARQ retransmission performance appears more noticeably particularlywhen the UL-DL configuration is changed with a high frequency as shownin method (3).

An object of the present invention is to provide a terminal apparatusand a buffer dividing method capable of reducing deterioration of HARQretransmission performance by continuing DL HARQ processes for downlinkdata before and after a change of a UL-DL configuration (ratio betweenUL subframes and DL subframes).

Solution to Problem

A terminal apparatus according to an aspect of the present invention isa terminal apparatus capable of changing a setting of a configurationpattern of subframes forming one frame, the configuration patternincluding a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the terminal apparatus including: a decoding section thatstores downlink data transmitted from a base station apparatus in abuffer for retransmission and decodes the downlink data; and atransmitting section that transmits a response signal generated using anerror detection result of the downlink data, in which the buffer isdivided into a plurality of regions for each retransmission processbased on a maximum value among numbers of retransmission processesrespectively defined in a plurality of the configuration patternscapable of being set in the terminal apparatus.

A buffer dividing method according to an aspect of the present inventionis a method for a terminal apparatus capable of changing a setting of aconfiguration pattern of subframes forming one frame, the configurationpattern including a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the buffer dividing method including: storing downlinkdata transmitted from a base station apparatus in a buffer forretransmission; decoding the downlink data; and transmitting a responsesignal generated using an error detection result of the downlink data,in which the buffer is divided into a plurality of regions for eachretransmission process based on a maximum value among numbers ofretransmission processes respectively defined in a plurality of theconfiguration patterns capable of being set in the terminal apparatus.

Advantageous Effects of Invention

According to the present invention, it is possible to reducedeterioration of HARQ retransmission performance by continuing DL HARQprocesses for downlink data before and after a change of a UL-DLconfiguration (ratio between UL subframes and DL subframes).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a method of spreading response signalsand reference signals;

FIG. 2 is a diagram illustrating an operation related to a case whereTDM is applied to response signals and uplink data on PUSCH resources;

FIG. 3 is a diagram provided for describing a UL-DL configuration inTDD;

FIG. 4 is a diagram provided for describing calculation of an IR buffersize;

FIG. 5 is a diagram illustrating a maximum number of DL HARQ processescorresponding to a UL-DL configuration;

FIG. 6 is a diagram provided for describing problems involved in achange of a UL-DL configuration;

FIG. 7 is a block diagram illustrating a main configuration of aterminal according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 9 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 10 is a diagram illustrating a method of dividing a soft bufferaccording to Embodiment 1 of the present invention;

FIG. 11 is a diagram illustrating a method of dividing a soft bufferaccording to Embodiment 1 of the present invention;

FIGS. 12A and 12B are diagrams illustrating a method of using an excessIR buffer region according to Embodiment 2 of the present invention;

FIG. 13 is a diagram provided for describing problems involved in memoryaccess according to Embodiment 3 of the present invention;

FIG. 14 is a diagram illustrating an example of a method of using anexcess IR buffer region according to Embodiment 3 of the presentinvention;

FIG. 15 is a diagram illustrating an example of a method of using anexcess IR buffer region according to Embodiment 3 of the presentinvention;

FIG. 16 is a diagram provided for describing an effect of memory accessaccording to Embodiment 3 of the present invention; and

FIG. 17 is a diagram provided for describing a concept of a simplememory access method according to Embodiment 3 of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numeralsand any duplicate description of the elements is omitted.

Embodiment 1

FIG. 7 is a main configuration diagram of terminal 200 according to thepresent embodiment. Terminal 200 can change a setting of a configurationpattern (UL-DL configuration) which is a configuration pattern ofsubframes forming one frame and which includes downlink communicationsubframes (DL subframes) used for downlink communication and uplinkcommunication subframes (UL subframe) used for uplink communication. Interminal 200, decoding section 210 stores downlink data transmitted froma base station in a retransmission buffer (soft buffer), decodes thedownlink data and radio transmitting section 222 transmits responsesignals generated using error detection results of the downlink data.Here, the above soft buffer is divided into a plurality of regions (IRbuffers) for each retransmission process based on a maximum value amonga number of retransmission processes (maximum number of DL HARQprocesses) defined for each of a plurality of configuration patternsthat can be set in terminal 200.

Hereinafter, a case will be described where one downlink componentcarrier is set in terminal 200 for simplicity of description. A casewill be described where no MIMO (Multiple Input Multiple Output) is setin terminal 200 (non-MIMO). That is, in equation 1, suppose K_(C)=1 (onedownlink component carrier is used) and K_(MIMO)=1 (non-MIMO, the numberof multiplexed layers: 1). That is, the following description will focuson the maximum number of DL HARQ processes (M_(DL_HARQ)) shown inequation 1.

(Configuration of Base Station)

FIG. 8 is a configuration diagram of base station 100 according toEmbodiment 1 of the present invention. In FIG. 8, base station 100includes control section 101, control information generating section102, coding section 103, modulation section 104, coding section 105,data transmission controlling section 106, modulation section 107,mapping section 108, inverse fast Fourier transform (IFFT) section 109,CP adding section 110, radio transmitting section 111, radio receivingsection 112, CP removing section 113, PUCCH extracting section 114,despreading section 115, sequence controlling section 116, correlationprocessing section 117, A/N determining section 118, bundled A/Ndespreading section 119, inverse discrete Fourier transform (IDFT)section 120, bundled A/N determining section 121 and retransmissioncontrol signal generating section 122.

Control section 101 assigns a downlink resource for transmitting controlinformation (i.e., downlink control information assignment resource) anda downlink resource for transmitting downlink data (i.e., downlink dataassignment resource) for a resource assignment target terminal(hereinafter, referred to as “destination terminal” or simply“terminal”) 200. This resource assignment is performed in a downlinkcomponent carrier included in a component carrier group configured forresource assignment target terminal 200. In addition, the downlinkcontrol information assignment resource is selected from among theresources corresponding to downlink control channel (i.e., PDCCH) ineach downlink component carrier. Moreover, the downlink data assignmentresource is selected from among the resources corresponding to downlinkdata channel (i.e., PDSCH) in each downlink component carrier. Inaddition, when there are a plurality of resource assignment targetterminals 200, control section 101 assigns different resources toresource assignment target terminals 200, respectively.

The downlink control information assignment resources are equivalent toL1/L2 CCH described above. To put it more specifically, the downlinkcontrol information assignment resources are each formed of one or aplurality of CCEs.

Control section 101 determines the coding rate used for transmittingcontrol information to resource assignment target terminal 200. The datasize of the control information varies depending on the coding rate.Thus, control section 101 assigns a downlink control informationassignment resource having the number of CCEs that allows the controlinformation having this data size to be mapped to the resource.

Control section 101 outputs information on the downlink data assignmentresource to control information generating section 102. Moreover,control section 101 outputs information on the coding rate to codingsection 103. In addition, control section 101 determines and outputs thecoding rate of transmission data (i.e., downlink data) to coding section105. Moreover, control section 101 outputs information on the downlinkdata assignment resource and downlink control information assignmentresource to mapping section 108. However, control section 101 controlsthe assignment in such a way that the downlink data and downlink controlinformation for the downlink data are mapped to the same downlinkcomponent carrier.

Control information generating section 102 generates and outputs controlinformation including the information on the downlink data assignmentresource to coding section 103. This control information is generatedfor each downlink component carrier. In addition, when there are aplurality of resource assignment target terminals 200, the controlinformation includes the terminal ID of each destination terminal 200 inorder to distinguish resource assignment target terminals 200 from oneanother. For example, the control information includes CRC bits maskedby the terminal ID of destination terminal 200. This control informationmay be referred to as “control information carrying downlink assignment”or “downlink control information (DCI).” Control information generatingsection 102 references, for example, the retransmission control signal(not shown) generated by retransmission control signal generatingsection 122 and includes, in the control information, retransmissioninformation indicating whether transmission of downlink data whosetransmission is controlled by data transmission controlling section 106is initial transmission or retransmission.

Coding section 103 encodes the control information using the coding ratereceived from control section 101 and outputs the coded controlinformation to modulation section 104.

Modulation section 104 modulates the coded control information andoutputs the resultant modulation signals to mapping section 108.

Coding section 105 uses the transmission data (i.e., downlink data) foreach destination terminal 200 and the coding rate information fromcontrol section 101 as input and encodes and outputs the transmissiondata to data transmission controlling section 106.

Data transmission controlling section 106 outputs the coded transmissiondata to modulation section 107 and also keeps the coded transmissiondata at the initial transmission. The coded transmission data is keptfor each destination terminal 200.

Furthermore, upon reception of a NACK or DTX for downlink datatransmitted on a certain downlink component carrier from retransmissioncontrol signal generating section 122, data transmission controllingsection 106 outputs the data kept in the manner described above andcorresponding to this downlink component carrier to modulation section107. Upon reception of an ACK for the downlink data transmitted on acertain downlink component carrier from retransmission control signalgenerating section 122, data transmission controlling section 106deletes the data kept in the manner described above and corresponding tothis downlink component carrier.

Modulation section 107 modulates the coded transmission data receivedfrom data transmission controlling section 106 and outputs the resultantmodulation signals to mapping section 108.

Mapping section 108 maps the modulation signals of the controlinformation received from modulation section 104 to the resourceindicated by the downlink control information assignment resourcereceived from control section 101 and outputs the resultant modulationsignals to IFFT section 109.

Mapping section 108 maps the modulation signals of the transmission datareceived from modulation section 107 to the resource (i.e., PDSCH (i.e.,downlink data channel)) indicated by the downlink data assignmentresource received from control section 101 (i.e., information includedin the control information) and outputs the resultant modulation signalsto IFFT section 109.

The control information and transmission data mapped to a plurality ofsubcarriers in a plurality of downlink component carriers in mappingsection 108 is transformed into time-domain signals fromfrequency-domain signals in IFFT section 109, and CP adding section 110adds a CP to the time-domain signals to form OFDM signals. The OFDMsignals undergo transmission processing such as digital to analog (D/A)conversion, amplification and up-conversion and/or the like in radiotransmitting section 111 and are transmitted to terminal 200 via anantenna.

Radio receiving section 112 receives, via an antenna, the uplinkresponse signals or reference signals transmitted from terminal 200, andperforms reception processing such as down-conversion, A/D conversionand/or the like on the uplink response signals or reference signals.

CP removing section 113 removes the CP added to the uplink responsesignals or reference signals from the uplink response signals orreference signals that have undergone the reception processing.

PUCCH extracting section 114 extracts, from the PUCCH signals includedin the received signals, the signals in the PUCCH region correspondingto the bundled ACK/NACK resource previously indicated to terminal 200.To put it more specifically, PUCCH extracting section 114 extracts thedata part of the PUCCH region corresponding to the bundled ACK/NACKresource (i.e., SC-FDMA symbols on which the bundled ACK/NACK resourceis assigned) and the reference signal part of the PUCCH region (i.e.,SC-FDMA symbols on which the reference signals for demodulating thebundled ACK/NACK signals are assigned). PUCCH extracting section 114outputs the extracted data part to bundled A/N despreading section 119and outputs the reference signal part to despreading section 115-1.

In addition, PUCCH extracting section 114 extracts, from the PUCCHsignals included in the received signals, a plurality of PUCCH regionscorresponding to an A/N resource associated with a CCE that has beenoccupied by the PDCCH used for transmission of the downlink assignmentcontrol information (DCI), and corresponding to a plurality of A/Nresources previously indicated to terminal 200. The A/N resource hereinrefers to the resource to be used for transmission of an A/N. To put itmore specifically, PUCCH extracting section 114 extracts the data partof the PUCCH region corresponding to the A/N resource (i.e., SC-FDMAsymbols on which the uplink control signals are assigned) and thereference signal part of the PUCCH region (i.e., SC-FDMA symbols onwhich the reference signals for demodulating the uplink control signalsare assigned). PUCCH extracting section 114 outputs both of theextracted data part and reference signal part to despreading section115-2. In this manner, the response signals are received on the resourceselected from the PUCCH resource associated with the CCE and thespecific PUCCH resource previously indicated to terminal 200.

Sequence controlling section 116 generates a base sequence that may beused for spreading each of the A/N indicated from terminal 200, thereference signals for the A/N, and the reference signals for the bundledACK/NACK signals (i.e., length-12 ZAC sequence). In addition, sequencecontrolling section 116 identifies a correlation window corresponding toa resource on which the reference signals may be assigned (hereinafter,referred to as “reference signal resource”) in PUCCH resources that maybe used by terminal 200. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource on which the reference signals may be assignedin bundled ACK/NACK resources and the base sequence to correlationprocessing section 117-1. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource and the base sequence to correlationprocessing section 117-1. In addition, sequence controlling section 116outputs the information indicating the correlation window correspondingto the A/N resources on which an A/N and the reference signals for theA/N are assigned and the base sequence to correlation processing section117-2.

Despreading section 115-1 and correlation processing section 117-1perform processing on the reference signals extracted from the PUCCHregion corresponding to the bundled ACK/NACK resource.

To put it more specifically, despreading section 115-1 despreads thereference signal part using a Walsh sequence to be used insecondary-spreading for the reference signals of the bundled ACK/NACKresource by terminal 200 and outputs the despread signals to correlationprocessing section 117-1.

Correlation processing section 117-1 uses the information indicating thecorrelation window corresponding to the reference signal resource andthe base sequence and thereby finds a correlation value between thesignals received from despreading section 115-1 and the base sequencethat may be used in primary-spreading in terminal 200. Correlationprocessing section 117-1 outputs the correlation value to bundled A/Ndetermining section 121.

Despreading section 115-2 and correlation processing section 117-2perform processing on the reference signals and A/Ns extracted from theplurality of PUCCH regions corresponding to the plurality of A/Nresources.

To put it more specifically, despreading section 115-2 despreads thedata part and reference signal part using a Walsh sequence and a DFTsequence to be used in secondary-spreading for the data part andreference signal part of each of the A/N resources by terminal 200, andoutputs the despread signals to correlation processing section 117-2.

Correlation processing section 117-2 uses the information indicating thecorrelation window corresponding to each of the A/N resources and thebase sequence and thereby finds a correlation value between the signalsreceived from despreading section 115-2 and a base sequence that may beused in primary-spreading by terminal 200. Correlation processingsection 117-2 outputs each correlation value to A/N determining section118.

A/N determining section 118 determines, on the basis of the plurality ofcorrelation values received from correlation processing section 117-2,which of the A/N resources is used to transmit the signals from terminal200 or none of the A/N resources is used. When determining that thesignals are transmitted using one of the A/N resources from terminal200, A/N determining section 118 performs coherent detection using acomponent corresponding to the reference signals and a componentcorresponding to the A/N and outputs the result of coherent detection toretransmission control signal generating section 122. Meanwhile, whendetermining that terminal 200 uses none of the A/N resources, A/Ndetermining section 118 outputs the determination result indicating thatnone of the A/N resources is used to retransmission control signalgenerating section 122.

Bundled A/N despreading section 119 despreads, using a DFT sequence, thebundled ACK/NACK signals corresponding to the data part of the bundledACK/NACK resource received from PUCCH extracting section 114 and outputsthe despread signals to IDFT section 120.

IDFT section 120 transforms the bundled ACK/NACK signals in thefrequency-domain received from bundled A/N despreading section 119 intotime-domain signals by IDFT processing and outputs the bundled ACK/NACKsignals in the time-domain to bundled A/N determining section 121.

Bundled A/N determining section 121 demodulates the bundled ACK/NACKsignals corresponding to the data part of the bundled ACK/NACK resourcereceived from IDFT section 120, using the reference signal informationon the bundled ACK/NACK signals that is received from correlationprocessing section 117-1. In addition, bundled A/N determination section121 decodes the demodulated bundled ACK/NACK signals and outputs theresult of decoding to retransmission control signal generating section122 as the bundled A/N information. However, when the correlation valuereceived from correlation processing section 117-1 is smaller than athreshold, and bundled A/N determining section 121 thus determines thatterminal 200 does not use any bundled A/N resource to transmit thesignals, bundled A/N determining section 121 outputs the result ofdetermination to retransmission control signal generating section 122.

Retransmission control signal generating section 122 determines whetheror not to retransmit the data transmitted on the downlink componentcarrier (i.e., downlink data) on the basis of the information inputtedfrom bundled A/N determining section 121 and the information inputtedfrom A/N determining section 118 and generates retransmission controlsignals based on the result of determination. To put it morespecifically, when determining that downlink data transmitted on acertain downlink component carrier needs to be retransmitted,retransmission control signal generating section 122 generatesretransmission control signals indicating a retransmission command forthe downlink data and outputs the retransmission control signals to datatransmission controlling section 106. In addition, when determining thatthe downlink data transmitted on a certain downlink component carrierdoes not need to be retransmitted, retransmission control signalgenerating section 122 generates retransmission control signalsindicating not to retransmit the downlink data transmitted on thedownlink component carrier and outputs the retransmission controlsignals to data transmission controlling section 106.

(Configuration of Terminal)

FIG. 9 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. In FIG. 9, terminal 200 includes radioreceiving section 201, CP removing section 202, fast Fourier transform(FFT) section 203, extraction section 204, demodulation section 205,decoding section 206, determination section 207, control section 208,demodulation section 209, decoding section 210, CRC section 211,response signal generating section 212, coding and modulation section213, primary-spreading sections 214-1 and 214-2, secondary-spreadingsections 215-1 and 215-2, DFT section 216, spreading section 217, IFFTsections 218-1, 218-2 and 218-3, CP adding sections 219-1, 219-2 and219-3, time-multiplexing section 220, selection section 221 and radiotransmitting section 222.

Radio receiving section 201 receives, via an antenna, OFDM signalstransmitted from base station 100 and performs reception processing suchas down-conversion, A/D conversion and/or the like on the received OFDMsignals. It should be noted that, the received OFDM signals includePDSCH signals assigned to a resource in a PDSCH (i.e., downlink data),or PDCCH signals assigned to a resource in a PDCCH.

CP removing section 202 removes a CP that has been added to the OFDMsignals from the OFDM signals that have undergone the receptionprocessing.

FFT section 203 transforms the received OFDM signals intofrequency-domain signals by FFT processing and outputs the resultantreceived signals to extraction section 204.

Extraction section 204 extracts, from the received signals to bereceived from FFT section 203, downlink control channel signals (i.e.,PDCCH signals) in accordance with coding rate information to bereceived. To put it more specifically, the number of CCEs forming adownlink control information assignment resource varies depending on thecoding rate.

Thus, extraction section 204 uses the number of CCEs that corresponds tothe coding rate as units of extraction processing, and extracts downlinkcontrol channel signals. In addition, the downlink control channelsignals are extracted for each downlink component carrier. The extracteddownlink control channel signals are outputted to demodulation section205.

Extraction section 204 extracts downlink data (i.e., downlink datachannel signals (i.e., PDSCH signals)) from the received signals on thebasis of information on the downlink data assignment resource intendedfor terminal 200 to be received from determination section 207 to bedescribed, hereinafter, and outputs the downlink data to demodulationsection 209. As described above, extraction section 204 receives thedownlink assignment control information (i.e., DCI) mapped to the PDCCHand receives the downlink data on the PDSCH.

Demodulation section 205 demodulates the downlink control channelsignals received from extraction section 204 and outputs the obtainedresult of demodulation to decoding section 206.

Decoding section 206 decodes the result of demodulation received fromdemodulation section 205 in accordance with the received coding rateinformation and outputs the obtained result of decoding to determinationsection 207.

Determination section 207 performs blind-determination (i.e.,monitoring) to find out whether or not the control information includedin the result of decoding received from decoding section 206 is thecontrol information intended for terminal 200. This determination ismade in units of decoding results corresponding to the units ofextraction processing. For example, determination section 207 demasksthe CRC bits by the terminal ID of terminal 200 and determines that thecontrol information resulted in CRC=OK (no error) as the controlinformation intended for terminal 200. Determination section 207 outputsinformation on the downlink data assignment resource intended forterminal 200, which is included in the control information intended forterminal 200, to extraction section 204.

Furthermore, determination section 207 outputs retransmissioninformation included in the control information intended for terminal200 indicating whether transmission of downlink data to terminal 200 isinitial transmission or retransmission to decoding section 210.

In addition, when detecting the control information (i.e., downlinkassignment control information) intended for terminal 200, determinationsection 207 informs control section 208 that ACK/NACK signals will begenerated (or are present). Moreover, when detecting the controlinformation intended for terminal 200 from PDCCH signals, determinationsection 207 outputs information on a CCE that has been occupied by thePDCCH to control section 208.

Control section 208 identifies the A/N resource associated with the CCEon the basis of the information on the CCE received from determinationsection 207. Control section 208 outputs, to primary-spreading section214-1, a base sequence and a cyclic shift value corresponding to the A/Nresource associated with the CCE or the A/N resource previouslyindicated by base station 100, and also outputs a Walsh sequence and aDFT sequence corresponding to the A/N resource to secondary-spreadingsection 215-1. In addition, control section 208 outputs the frequencyresource information on the A/N resource to IFFT section 218-1.

When determining to transmit bundled ACK/NACK signals using a bundledACK/NACK resource, control section 208 outputs the base sequence andcyclic shift value corresponding to the reference signal part (i.e.,reference signal resource) of the bundled ACK/NACK resource previouslyindicated by base station 100 to primary-despreading section 214-2 andoutputs a Walsh sequence to secondary-despreading section 215-2. Inaddition, control section 208 outputs the frequency resource informationon the bundled ACK/NACK resource to IFFT section 218-2.

Control section 208 outputs a DFT sequence used for spreading the datapart of the bundled ACK/NACK resource to spreading section 217 andoutputs the frequency resource information on the bundled ACK/NACKresource to IFFT section 218-3.

Control section 208 selects the bundled ACK/NACK resource or the A/Nresource and instructs selection section 221 to output the selectedresource to radio transmitting section 222. Moreover, control section208 instructs response signal generating section 212 to generate thebundled ACK/NACK signals or the ACK/NACK signals in accordance with theselected resource.

Demodulation section 209 demodulates the downlink data received fromextraction section 204 and outputs the demodulated downlink data (LLR)to decoding section 210.

When the retransmission information received from determination section207 indicates initial transmission, decoding section 210 stores thedownlink data (LLR) received from demodulation section 209 in theretransmission buffer (soft buffer). Decoding section 210 furtherdecodes the downlink data received from demodulation section 209 andoutputs the decoded downlink data to CRC section 211. On the other hand,when the retransmission information received from determination section207 indicates retransmission, decoding section 210 combines the downlinkdata received from demodulation section 209 and the downlink data readfrom the retransmission buffer and stores the combined downlink data inthe retransmission buffer again. Moreover, decoding section 210 decodesthe combined downlink data and outputs the decoded downlink data to CRCsection 211. Details of the method of calculating a retransmissionbuffer size (dividing method) and the method of storing downlink data inthe retransmission buffer will be described later.

CRC section 211 performs error detection on the decoded downlink datareceived from decoding section 210, for each downlink component carrierusing CRC and outputs an ACK when CRC=OK (no error) or outputs a NACKwhen CRC=Not OK (error) to response signal generating section 212.Moreover, CRC section 211 outputs the decoded downlink data as thereceived data when CRC=OK (no error).

Response signal generating section 212 generates response signals on thebasis of the reception condition of downlink data (i.e., result of errordetection on downlink data) on each downlink component carrier inputtedfrom CRC section 211 and information indicating a predetermined groupnumber. To put it more specifically, when instructed to generate thebundled ACK/NACK signals from control section 208, response signalgenerating section 212 generates the bundled ACK/NACK signals includingthe results of error detection for the respective component carriers asindividual pieces of data. Meanwhile, when instructed to generateACK/NACK signals from control section 208, response signal generatingsection 212 generates ACK/NACK signals of one symbol. Response signalgenerating section 212 outputs the generated response signals to codingand modulation section 213.

Upon reception of the bundled ACK/NACK signals, coding and modulationsection 213 encodes and modulates the received bundled ACK/NACK signalsto generate the modulation signals of 12 symbols and outputs themodulation signals to DFT section 216. In addition, upon reception ofthe ACK/NACK signals of one symbol, coding and modulation section 213modulates the ACK/NACK signals and outputs the modulation signals toprimary-spreading section 214-1.

Primary-spreading sections 214-1 and 214-2 corresponding to the A/Nresources and reference signal resources of the bundled ACK/NACKresources spread the ACK/NACK signals or reference signals using thebase sequence corresponding to the resources in accordance with theinstruction from control section 208 and output the spread signals tosecondary-spreading sections 215-1 and 215-2.

Secondary-spreading sections 215-1 and 215-2 spread the receivedprimary-spread signals using a Walsh sequence or a DFT sequence inaccordance with an instruction from control section 208 and outputs thespread signals to IFFT sections 218-1 and 218-2.

DFT section 216 performs DFT processing on 12 time-series sets ofreceived bundled ACK/NACK signals to obtain 12 signal components in thefrequency-domain. DFT section 216 outputs the 12 signal components tospreading section 217.

Spreading section 217 spreads the 12 signal components received from DFTsection 216 using a DFT sequence indicated by control section 208 andoutputs the spread signal components to IFFT section 218-3.

IFFT sections 218-1, 218-2 and 218-3 perform IFFT processing on thereceived signals in association with the frequency positions where thesignals are to be allocated, in accordance with an instruction fromcontrol section 208. Accordingly, the signals inputted to IFFT sections218-1, 218-2 and 218-3 (i.e., ACK/NACK signals, the reference signals ofA/N resource, the reference signals of bundled ACK/NACK resource andbundled ACK/NACK signals) are transformed into time-domain signals.

CP adding sections 219-1, 219-2 and 219-3 add the same signals as thelast part of the signals obtained by IFFT processing to the beginning ofthe signals as a CP.

Time-multiplexing section 220 time-multiplexes the bundled ACK/NACKsignals received from CP adding section 219-3 (i.e., signals transmittedusing the data part of the bundled ACK/NACK resource) and the referencesignals of the bundled ACK/NACK resource to be received from CP addingsection 219-2 on the bundled ACK/NACK resource and outputs themultiplexed signals to selection section 221.

Selection section 221 selects one of the bundled ACK/NACK resourcereceived from time-multiplexing section 220 and the A/N resourcereceived from CP adding section 219-1 and outputs the signals assignedto the selected resource to radio transmitting section 222.

Radio transmitting section 222 performs transmission processing such asD/A conversion, amplification and up-conversion and/or the like on thesignals received from selection section 221 and transmits the resultantsignals to base station 100 via an antenna.

[Operations of Base Station 100 and Terminal 200]

Operations of base station 100 and terminal 200 having theabove-described configurations will be described.

Base station 100 indicates to terminal 200 beforehand a set of UL-DLconfigurations that can be set. This set of UL-DL configurations thatcan be set is information indicating UL-DL configurations changeablethrough TDD eIMTA.

Terminal 200 divides a soft buffer into equal portions: a plurality ofIR buffers based on the maximum number of DL HARQ processes which islargest among a maximum number of DL HARQ processes defined in eachUL-DL configuration of the set of UL-DL configurations that can be set.The IR buffer size is determined in this manner.

The method of calculating the IR buffer size (N_(IR)) in terminal 200will be described using FIG. 10 and FIG. 11, and equation 2. In thefollowing description, it is assumed in equation 2 that K_(C)=1 (onedownlink component carrier is used) and K_(MIMO)=1 (non-MIMO).

$\begin{matrix}{( {{Equation}\mspace{14mu} 2} )\mspace{616mu}} & \; \\{N_{IR} = \lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min ( {{\max ( M_{{{DL}\; \_ \; {HARQ}},{{eIMTA}\; \_ \; {Config}}} )},M_{limit}} )}} \rfloor} & \lbrack 2\rbrack\end{matrix}$

In FIG. 10 and FIG. 11, a set of UL-DL configurations changeable throughTDD eIMTA (eIMTA_Config) in terminal 200 may be expressed as UL-DLconfiguration#0 (hereinafter, may also be expressed as “Config#0,” thesame applies to other UL-DL configurations) Config#1, and Config#6 (thatis, eIMTA_Config={#0, #1, #6}).

FIG. 10 illustrates a maximum number of DL HARQ processes (M_(DL_HARQ))defined in each UL-DL configuration. As shown in FIG. 10, the maximumnumbers of DL HARQ processes defined in Config#0, Config#1 and Config#6which are eIMTA_Configs of terminal 200 are 4, 7 and 6 respectively.That is, M_(DL_HARQ,eIMTA_Config) shown in equation 2={4, 6, 7}.

Therefore, the maximum number of DL HARQ processes (maximum value) whichis largest among the maximum numbers of DL HARQ processes defined ineach UL-DL configuration of the set of UL-DL configurations changeableis 7. That is, max(M_(DL_HARQ,eIMTA_Config)) shown in equation 2=7.

The soft buffer (buffer capacity: N_(soft)) is divided into equalportions: a number of IR buffers (here, divided into 7 portions)corresponding to a maximum value (max(M_(DL_HARQ,eIMTA_Config))=7) ofthe maximum number of DL HARQ processes or a maximum allowable value(M_(limit)=8) of the number of DL HARQ processes that can be supportedby terminal 200, whichever is the smaller(min(max(M_(DL_HARQ,eIMTA_Config)),M_(limit))−7).

FIG. 11 illustrates an example of the soft buffer dividing method in thecase where the UL-DL configuration in terminal 200 in whicheIMTA_Config={#0, #1, #6} is set is changed from Config#0 to Config#1.

The maximum number of DL HARQ processes differs between the differentUL-DL configurations before and after the change. However, as describedabove, the soft buffer possessed by terminal 200 is divided into sevenequal portions (N_(IR)=N_(soft)/7) regardless of the UL-DLconfigurations before and after the change.

The respective DL HARQ processes in the UL-DL configuration are assignedto IR buffers (IR buffer group) corresponding to the maximum number ofDL HARQ processes defined in the UL-DL configuration set in terminal 200at a present point in time among the seven IR buffers. To put it morespecifically, as shown in FIG. 11, DL HARQ processes of DL HARQ processnumbers 1 to 4 are respectively assigned to the first to fourth IRbuffers (corresponding to the maximum number of DL HARQ processesdefined in Config#0) from the left among the seven IR buffers obtainedby dividing the soft buffer into seven portions before the change(Config#0). Similarly, DL HARQ processes of DL HARQ process numbers 1 to7 are assigned to the seven IR buffers (corresponding to the maximumnumber of DL HARQ processes defined in Config#1) after the change(Config#1).

That is, as shown in FIG. 11, before the change (Config#0), terminal 200executes DL HARQ using four IR buffers corresponding to the maximumnumber of DL HARQ processes defined in Config#0 among the seven IRbuffers. On the other hand, as shown in FIG. 11, after the change(Config#1), terminal 200 executes DL HARQ using all of the seven IRbuffers (corresponding to the maximum number of DL HARQ processesdefined in Config#1).

Thus, although the maximum number of DL HARQ processes differs beforethe change (Config#0) and after the change (Config#1), the positions inthe IR buffer (positions in which downlink data is arranged) relating tothe DL HARQ processes of DL HARQ process numbers 1 to 4 are the same.Therefore, terminal 200 can correctly read downlink data (LLR) of thesame DL HARQ process (DL HARQ process number 2 in FIG. 11) stored in theIR buffer at the same position on the soft buffer before and after thechange of the UL-DL configuration. That is, terminal 200 can continuethe DL HARQ processes even before and after the change of the UL-DLconfiguration.

Note that as shown in FIG. 11, of the maximum number of DL HARQprocesses defined in each UL-DL configuration of the set of UL-DLconfigurations that can be set in terminal 200, when the maximum numberof DL HARQ processes (e.g., 4 in Config#0) defined in the UL-DLconfiguration being used by terminal 200 is smaller than the maximumnumber of DL HARQ processes (e.g., 7 in FIG. 10 and FIG. 11) which islargest, IR buffers corresponding to the numbers of DL HARQ processescorresponding to the difference thereof (IR buffer regions indicated byN/A (Not Available) shown in FIG. 11) are not used. That is, of theplurality of IR buffers obtained by dividing the soft buffer, remainingIR buffers other than the IR buffers assigned to the respective DL HARQprocesses of the UL-DL configuration set in terminal 200 at a currentpoint in time are not used. Hereinafter, the above-described IR bufferregions not used may be called “excess IR buffer regions.”

As described above, in the present embodiment, terminal 200 divides thesoft buffer into a plurality of IR buffers for each DL HARQ processbased on a maximum value in the maximum number of DL HARQ processesdefined in the UL-DL configurations that can be set in terminal 200. Byso doing, terminal 200 can correctly read data stored in the IR bufferscorresponding to the same DL HARQ process before and after the change ofthe UL-DL configuration when at least one UL-DL configuration is lessthan 8 (M_(limit)) (in FIG. 10, when it is changeable to one of theUL-DL configurations of Config#0, Config#1 and Config#6) of the maximumnumber of DL HARQ processes defined in the respective UL-DLconfigurations that can be set in terminal 200. That is, terminal 200can continue DL HARQ before and after the change of the UL-DLconfiguration. Thus, according to the present embodiment, it is possibleto reduce deterioration of the HARQ retransmission performance bycontinuing DL HARQ processes on downlink data before and after thechange of the UL-DL configuration.

Embodiment 2

A case has been described in Embodiment 1 where no excess IR bufferregion is used. In contrast, a method of effectively using excess IRbuffer regions will be described in Embodiment 2.

Hereinafter, method 1 (FIG. 12A) and method 2 (FIG. 12B) for usingexcess IR buffer regions will be described.

In the following description, as with Embodiment 1, a set of UL-DLconfigurations changeable by TDD eIMTA for terminal 200 is assumed to beConfig#0, Config#1 and Config#6 (that is, eIMTA_Config={#0, #1, #6}).That is, as shown in FIG. 12A and FIG. 12B, a soft buffer in terminal200 is divided into seven portions.

That is, in use method 1 (FIG. 12A), excess IR buffer regions (three IRbuffers) are generated before the change of the UL-DL configuration(Config#0: maximum number of DL HARQ processes: 4). On the other hand,in use method 2 (FIG. 12B), excess IR buffer regions (three IR buffers)are generated after the change of the UL-DL configuration (Config#0).

<Use Method 1>

In FIG. 12A, terminal 200 uses the excess IR buffer regions asadditional IR buffer regions for DL HARQ processes existing in a UL-DLconfiguration in use. To put it more specifically, in FIG. 12A, terminal200 uses three excess IR buffer regions as additional IR buffer regionsfor three DL HARQ processes (DL HARQ process numbers 1 to 3) of the fourDL HARQ processes (DL HARQ process numbers 1 to 4) existing in Config#0being used by terminal 200.

That is, a number of DL HARQ processes (3 processes in FIG. 12A)corresponding to the difference between the total number of IR buffers(7 in FIG. 12A) obtained by dividing the soft buffer and a maximumnumber of DL HARQ processes (4 in FIG. 12A) defined in the UL-DLconfiguration in use are assigned to the excess IR buffer regions.

This allows terminal 200 to use two IR buffers for DL HARQ processes ofDL HARQ process numbers 1 to 3.

When instructed from base station 100 to change the UL-DL configuration,terminal 200 resets downlink data stored in the excess IR buffer regions(additional IR buffer regions).

As described above, when the maximum number of DL HARQ processes definedin the UL-DL configuration set in terminal 200 at a current point intime is smaller than the number of IR buffers (the number of divisionsof the soft buffer), one of DL HARQ processes in the UL-DL configurationis assigned to remaining IR buffers (corresponding to a second regiongroup, that is, excess IR buffer regions) other than IR buffers(corresponding to a first region group) to which DL HARQ processes inthe UL-DL configuration have been assigned among a plurality of IRbuffers.

In this way, terminal 200 uses the excess IR buffer regions asadditional IR buffer regions for DL HARQ processes existing in the UL-DLconfiguration in use, and can thereby increase the IR buffer size per DLHARQ process. It is thereby possible to improve the error correctionperformance and improve the HARQ retransmission performance compared tothe case where no excess IR buffer region is used (e.g., see FIG. 11).

As in the case of Embodiment 1, terminal 200 can correctly read datastored in IR buffers corresponding to the same DL HARQ processes (DLHARQ process numbers 1 to 4 in FIG. 12A) (IR buffers other than excessIR buffer regions) before and after the change of the UL-DLconfiguration. For this reason, terminal 200 can continue DL HARQprocesses even if downlink data stored in the excess IR buffer regions(additional IR buffer regions) is reset due to the change of the UL-DLconfiguration.

A case has been described in FIG. 12A where a plurality of DL HARQprocesses existing in the UL-DL configuration in use are assigned to aplurality of additional IR buffer regions. However, only a single DLHARQ process existing in the UL-DL configuration in use may be assignedto the plurality of additional IR buffer regions.

A case has been described in FIG. 12A where the whole additional IRbuffer region has been divided into three equal portions (the same sizeas the IR buffer size) to be assigned to three DL HARQ processesrespectively, but the present invention is not limited to this. Forexample, the whole additional IR buffer region may be evenly re-dividedby the maximum number of DL HARQ processes defined in the UL-DLconfiguration in use (divided into four equal portions in Config#0 shownin FIG. 12A) and all DL HARQ processes in the UL-DL configuration may beassigned to the respective re-divided regions respectively.

As described above, the excess IR buffer regions may possibly be resetdue to an increase in the number of DL HARQ processes caused by thechange of the UL-DL configuration. Thus, when the excess IR bufferregions are used as additional IR buffer regions, terminal 200 may storeparity bits in the additional IR buffer regions preferentially. It isthereby possible to prevent systematic bits of a high degree ofimportance from being reset.

<Use Method 2>

In FIG. 12B, terminal 200 uses excess IR buffer regions as IR bufferregions for DL HARQ processes which are nonexistent in the UL-DLconfiguration in use. To put it more specifically, in FIG. 12B, terminal200 uses three excess IR buffer regions as IR buffer regionscorresponding to DL HARQ processes (DL HARQ process numbers 5 to 7)which are nonexistent in DL HARQ processes (DL HARQ process numbers 1 to4) of Config#0 being used by terminal 200 but existing in Config#1 usedby terminal 200 immediately before the change.

That is, when the maximum number of DL HARQ processes defined in theUL-DL configuration set in terminal 200 at a current point in time issmaller than the number of IR buffers (the number of divisions of thesoft buffer), DL HARQ processes assigned to within a regioncorresponding to the excess IR buffer regions among DL HARQ processes inthe UL-DL configuration set last in terminal 200 are continuouslyassigned to remaining IR buffers (corresponding to a second regiongroup, that is, excess IR buffer regions) other than IR buffers(corresponding to a first region group) to which the DL HARQ processesin the UL-DL configuration are assigned among the plurality of IRbuffers.

In this way, even when instructed from base station 100 to change theUL-DL configuration from Config#1 to Config#0, terminal 200 continues DLHARQ processes on excess IR buffer regions without resetting downlinkdata stored in the IR buffer regions (DL HARQ process numbers 5 to 7)which become the excess IR buffer regions.

As described above, terminal 200 uses the excess IR buffer regions as IRbuffer regions for DL HARQ processes which are nonexistent in the UL-DLconfiguration in use. Even when the number of DL HARQ processesdecreases due to the change of the UL-DL configuration in particular, itis thereby possible to continue DL HARQ in DL HARQ processescorresponding to the decrease. That is, terminal 200 can continue DLHARQ even when the DL HARQ processes corresponding to theabove-described decrease have not completed at the time of the change ofthe UL-DL configuration. Thus, compared to a case where no excess IRbuffer region is used (e.g., see FIG. 11), it is possible to improve theHARQ retransmission performance.

A case has been described in FIG. 12B where a plurality of DL HARQprocesses existing in the last set UL-DL configuration are assigned to aplurality of excess IR buffer regions. However, only a single DL HARQprocess existing in the last set UL-DL configuration may be assigned tothe plurality of excess IR buffer regions.

Use method 1 and use method 2 of excess IR buffer regions have beendescribed so far.

By this means, in the present embodiment, even when the maximum numberof DL HARQ processes defined in the UL-DL configuration being used byterminal 200 is smaller than the number of the plurality of IR buffers(the number of divisions of the soft buffer) obtained by dividing thesoft buffer, it is possible to effectively use IR buffers (excess IRbuffer regions) corresponding to the number of DL HARQ processescorresponding to the difference thereof. Compared to Embodiment 1, thepresent embodiment can thereby further improve the HARQ retransmissionperformance.

Regarding whether to use excess IR buffer regions as additional IRbuffer regions for DL HARQ processes existing in the UL-DL configurationin use (use method 1: FIG. 12A) or use excess IR buffer regions as IRbuffer regions for DL HARQ processes which are nonexistent in the UL-DLconfiguration in use (use method 2: FIG. 12B), one of the two may bedefined beforehand or switching between the two may be performed by asetting. For example, terminal 200 may set use method 2 (FIG. 12B) if DLHARQ processes before the change of the UL-DL configuration need to becontinued even after the change and set use method 1 (FIG. 12A) if DLHARQ processes before the change of the UL-DL configuration need not becontinued after the change.

Embodiment 3

A case will be described in the present embodiment where when excess IRbuffer regions are used as in the case of Embodiment 2, DL HARQprocesses to which excess IR buffer regions are assigned are furtherdefined.

Embodiment 2 (FIG. 12A and FIG. 12B) does not define what size of anexcess IR buffer region is assigned to which DL HARQ process. For thisreason, while resetting or continuation of DL HARQ processes (which maysimply be called “HARQ continuation”) is repeated for each IR buffer dueto a change of the UL-DL configuration, even if the UL-DL configurationis changed to the same UL-DL configuration again, the order of DL HARQprocess numbers assigned to excess IR buffer regions may be differentfrom the initially assigned order of DL HARQ process numbers.

For example, FIG. 13 illustrates assignment of DL HARQ processes inexcess IR buffer regions when the UL-DL configuration is changed inorder of Config#0, Config#1, Config#6, Config#0.

As shown in FIG. 13, at a point in time at which Config#0 is set first,DL HARQ processes are assigned to three excess IR buffer regions inorder of DL HARQ process numbers 1, 2, 3. Next, when the setting ischanged to Config#1, all the excess IR buffer regions are reset and thesetting is changed to Config#6, a DL HARQ process of DL HARQ processnumber 1 is assigned to one excess IR buffer region. When the setting ischanged to Config#1 again, the DL HARQ process of DL HARQ process number1 is continued in the excess IR buffer region which already existedbefore the setting change and DL HARQ processes are assigned to twonewly generated excess IR buffer regions in order of DL HARQ processnumbers 2 and 3 respectively.

That is, in FIG. 13, the order of DL HARQ processes assigned to excessIR buffer regions (order of DL HARQ process numbers 2, 3, 1) when resetto Config#0 becomes different from the order of DL HARQ processesassigned to excess IR buffer regions (order of DL HARQ process numbers1, 2, 3) when Config#0 is initially set. Thus, the order of DL HARQprocesses stored in excess IR buffer regions differs depending on thechange of the UL-DL configuration.

As a result, the example of FIG. 13 shows three cases of IR bufferscorresponding to DL HARQ process number 1 (including excess IR bufferregions): when only the first from the left is the IR buffer (Case 1:when Config#1 is set), when the first and fifth from the left are the IRbuffers (Case 2: when first Config#0 is set) and when the first andseventh from the left are the IR buffers (Case 3: when Config#6 is setand when Config#0 is reset). This means that processing of access to thesoft buffer in the terminal has been complicated.

Thus, the present embodiment will describe a method of simplifying theprocessing of access to the soft buffer in terminal 200.

FIGS. 14 and 15 illustrate a soft buffer configuration according to thepresent embodiment.

In the following description, as in the case of Embodiment 2, a set ofUL-DL configurations changeable by TDD eIMTA on terminal 200 is assumedto be Config#0, Config#1, Config#6 (that is, eIMTA_Config={#0, #1, #6}).That is, the soft buffer is divided into seven portions in terminal 200.

FIG. 14 illustrates a case where the UL-DL configuration is changed inorder of Config#0, Config#6, Config#1 and FIG. 15 illustrates a casewhere the UL-DL configuration is changed in order of Config#1, Config#6,Config#0. In FIGS. 14 and 15, a maximum of three excess IR bufferregions (fifth to seventh IR buffers from left) are generated whenConfig#0 is set and one excess IR buffer region (seventh IR buffer fromleft) is generated when Config#6 is set.

In the present embodiment, a plurality of IR buffers obtained bydividing the soft buffer are associated with DL HARQ processes in therespective UL-DL configurations beforehand.

To put it more specifically, in FIGS. 14 and 15, DL HARQ processes of DLHARQ process numbers 1 to 4 are associated with the first to fourth IRbuffers from the left of the seven IR buffers respectively.

In FIGS. 14 and 15, the DL HARQ process of DL HARQ process number 1 andthe DL HARQ process of DL HARQ process number 1 are associated with thefifth IR buffer from the left of the seven IR buffers. Likewise, the DLHARQ process of DL HARQ process number 6 and the DL HARQ process of DLHARQ process number 2 are associated with the sixth IR buffer from theleft. The DL HARQ process of DL HARQ process number 7 and the DL HARQprocess of DL HARQ process number 3 are associated with the seventh IRbuffer from the left.

That is, the IR buffer region associated with DL HARQ process number 5and the excess IR buffer region associated with DL HARQ process number 1become common IR buffers. Similarly, the IR buffer region associatedwith DL HARQ process number 6 and the excess IR buffer region associatedwith DL HARQ process #2 become common IR buffers. The IR buffer regionassociated with DL HARQ process number 7 and the excess IR buffer regionassociated with DL HARQ process #3 become common IR buffers. That is, inFIGS. 14 and 15, common IR buffer regions are assigned to DL HARQprocess number n (where, n=1, 2, 3) and DL HARQ process number n+4. Inother words, DL HARQ process numbers are fixedly associated with eachexcess IR buffer region regardless of the change of the UL-DLconfiguration.

FIG. 16 illustrates assignment of DL HARQ processes in excess IR bufferregions when the same change of the UL-DL configuration as in FIG. 13takes place to illustrate the effect of simplification of a memoryconfiguration in the present embodiment.

In FIG. 16, DL HARQ processes are always assigned to three excess IRbuffer regions in order of DL HARQ process numbers 1, 2, 3 respectivelyregardless of the UL-DL configuration. Thus, the example of FIG. 16shows two cases of the IR buffer corresponding to DL HARQ process number1 (including the excess IR buffer region): when only the first from theleft is the IR buffer (Case 1: when Config#1 is set) and when the firstand fifth from the left are the IR buffers (Case 2: when Config#0 isset). That is, while the number of positions that can be taken by the IRbuffer corresponding to DL HARQ process number 1 is 3 in FIG. 13, thenumber of positions can be reduced to 2 in the present embodiment. Thatis, in FIG. 16, it is possible to simplify processing of access to thesoft buffer in terminal 200 compared to FIG. 13.

FIG. 17 illustrates a conceptual diagram of correspondence between IRbuffers and DL HARQ process numbers.

In FIG. 17, an IR buffer obtained by dividing the soft buffer (buffercapacity N_(soft)) into 8 (=min(max(M_(DL_HARQ,eIMTA_Config)),M_(limit))) equal portions is assumed to be one unit (therefore,min(max(M_(DL_HARQ,eIMTA_Config)), M_(limit))=8 units in total). DL HARQprocess numbers are respectively assigned to DL HARQ processescorresponding to a maximum number of DL HARQ processes defined in eachUL-DL configuration in each of a plurality of UL-DL configurations thatcan be set in terminal 200 in ascending order from the same number (here‘1’). In FIG. 17, a minimum value (min(M_(DL_HARQ,eIMTA_Config))) in amaximum number of DL HARQ processes defined in a plurality of UL-DLconfigurations that can be set in terminal 200 is assumed to be 6processes. That is, the difference between the number of IR buffersobtained by dividing the soft buffer and the above-described minimumvalue (=min(max(M_(DL_HARQ,eIMTA_Config)),M_(limit))−min(min(M_(DL_HARQ,eIMTA_Config)), M_(limit))) is 2.

In FIG. 17, of 8 IR buffer units, 6 (=min(min(M_(DL_HARQ,eIMTA_Config)),M_(limit))) units are assigned to 6 (=min(min(M_(DL_HARQ,eIMTA_Config)),M_(limit))) DL HARQ processes (DL HARQ process numbers 1 to 6), one unitfor each DL HARQ process (correspondence indicated by a solid linearrow). That is, a number of DL HARQ processes corresponding to theabove-described minimum value are respectively fixedly associated with anumber of IR buffers (corresponding to the third region group)corresponding to a minimum value (6 processes) of the above-describedmaximum number of DL HARQ processes among a plurality of IR buffers inascending order from DL HARQ process number 1 to DL HARQ process number6.

On the other hand, of the 8 IR buffer units, the remaining 2(=min(max(M_(DL_HARQ,eIMTA_Config)), M_(limit))−min(min(M_(DL_HARQ,eIMTA_Config)), M_(limit))) units are assigned to theremaining 2 (=min(max(M_(DL_HARQ,eIMTA_Config)), M_(limit))−min(min(M_(DL_HARQ,eIMTA_Config)), M_(limit))) DL HARQ processes (DL HARQprocess numbers 7 and 8), and at the same time, are also assigned to 2(=min(max(M_(DL_HARQ,eIMTA_Config)),M_(limit))−min(min(M_(DL_HARQ,eIMTA_Config)), M_(limit))) DL HARQprocesses of the 6 (=min(min(M_(DL_HARQ,eIMTA_Config)), M_(limit))) DLHARQ processes which have already been assigned, one unit for each DLHARQ process (correspondence indicated by a dotted line arrow). That is,a number of DL HARQ processes corresponding to the above-describeddifference (2 processes) in ascending order from DL HARQ process number7 next to DL HARQ process number 6, and a number of DL HARQ processescorresponding to the above-described difference (2 processes) of the DLHARQ processes of DL HARQ process numbers 1 to 6 (here, DL HARQ processnumbers 1 and 2) are respectively fixedly associated with the remainingIR buffers (corresponding to the fourth region group) other than the IRbuffer (corresponding to the third region group) to which a number of DLHARQ processes corresponding to the above-described minimum value (6processes) among the plurality of IR buffers.

As described above, according to the present embodiment, accesspositions (buffer addresses) of the soft buffer corresponding to DL HARQprocess numbers are fixed regardless of the change of the UL-DLconfiguration. This makes it possible to simplify processing of accessto the soft buffer in terminal 200.

A case has been described in FIGS. 14 and 15 where DL HARQ processnumber n (where, n=1, 2, 3) and DL HARQ process number n+4 are assignedto a common IR buffer region. However, the combination of DL HARQprocess numbers assigned to the common IR buffer region is not limitedto this.

In FIG. 16, although the first IR buffer from the left and the fifth IRbuffer are located as positions dispersed from each other on the softbuffer, this is an example of logical arrangement (logical addresses) ofthe IR buffers and physical arrangement (physical addresses) of these IRbuffers may be arranged at neighboring positions on the soft buffer.

Parity bits may be preferentially stored in one IR buffer (that is,excess IR buffer region) unit common to one of DL HARQ processes #5 to#7 of the IR buffers corresponding to DL HARQ processes #1 to #4 shownin FIGS. 14 and 15. In this way, it is possible to prevent systematicbits of a high degree of importance from being reset due to a change ofthe UL-DL configuration.

The embodiments of the present invention have been described so far.

In the above embodiment, instead of indicating to terminal 200 a set ofUL-DL configurations changeable in terminal 200, base station 100 maycalculate min(max(M_(DL_HARQ,eIMTA_Config), M_(limit))) shown inequation 2 and indicate the calculation result to terminal 200. In thiscase, since the calculation result of min(max(M_(DL_HARQ,eIMTA_Config),M_(limit))) can take only 4, 6, 7 or 8, base station 100 may indicate2-bit information to terminal 200. Thus, it is possible to reduce thenumber of bits to be indicated to terminal 200 more than the number ofbits (3n (n≥2) bits) required to indicate the set of UL-DLconfigurations changeable.

In the above embodiment, considering that M_(limit)=8, that the maximumnumber of DL HARQ processes (M_(HARQ)) defined in the four UL-DLconfigurations (Config#2 to #5) of the seven UL-DL configurations aregreater than 8 (=M_(limit)) as shown in FIG. 5, and that the number ofUL-DL configurations changeable by eIMTA is plural, the calculationresult of min(max(M_(DL_HARQ,eIMTA_Config), M_(limit))) shown inequation 2 is likely to be 8 in many cases. Thus, base station 100 maynot indicate the set of UL-DL configurations changeable or thecalculation result of min(max(M_(DL_HARQ,eIMTA_Config), M_(limit))) toterminal 200 in which TDD eIMTA is set, and terminal 200 may calculatethe IR buffer size (N_(IR)) always assuming thatmin(max(M_(DL_HARQ,eIMTA_Config), M_(limit)))=8. That is, when TDD eIMTAis not set, terminal 200 may calculate the IR buffer size according toequation 1, and when TDD eIMTA is set, terminal 200 may calculate the IRbuffer size according to following equation 3. In this case, terminal200 can continue DL HARQ processes before and after the change of theUL-DL configuration without signaling to terminal 200 of the set ofUL-DL configurations changeable or the calculation result ofmin(max(M_(DL_HARQ,eIMTA_Config), M_(limit))) or the like.

$\begin{matrix}{( {{Equation}\mspace{14mu} 3} )\mspace{616mu}} & \; \\{N_{IR} = \lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot M_{limit}} \rfloor} & \lbrack 3\rbrack\end{matrix}$

A case has been described in the above embodiment where the soft bufferis divided by M_(DL_HARQ,eIMTA_Config) or M_(limit), whichever is thesmaller value according to equations 1 to 3. However, terminal 200 isnot limited to this, but the soft buffer may be divided, for example, bymax(M_(DL_HARQ,eIMTA_Config)) without using M_(limit) which is athreshold.

A case has been described in the above embodiment where M_(limit)=8 asshown in equations 1 to 3. This is a value corresponding to the maximumnumber of DL HARQ processes that can be handled by the base station(eNB), for example, in an FDD system. However, the value of M_(limit) isnot limited to 8. In a TDD system in particular, the maximum number ofDL HARQ processes that can be handled by base station 100 is greaterthan the maximum number of DL HARQ processes (8) that can be handled bythe base station in the FDD system. For example, in UL-DL Config#5, themaximum number of DL HARQ processes that can be handled by base station100 is 15. Thus, the value of M_(limit) may be any value not exceedingthe number of DL HARQ processes that can be handled by base station 100.

In the above embodiment, when DL HARQ processes are not continued, thiscase has been expressed as an IR buffer being “reset.” However, the IRbuffer need not actually be reset (flashed), and it is only necessary toprevent downlink data stored in the IR buffer from being read to be usedfor decoding. Therefore, it is only necessary to indicate whethertransmission is initial transmission or not in the DL HARQ processcorresponding to the IR buffer. A signal indicating whether transmissionis initial transmission or retransmission is indicated by an NDI (NewData Indicator) in downlink data assignment information (that is, DLassignment). When the NDI has a value inverted from a value at the timeof the previous reception in DL assignment indicating downlink data inthe DL HARQ process corresponding to the IR buffer, this indicatesinitial transmission, and when the NDI is not any inverted value, thisindicates retransmission.

Although an antenna has been described in the aforementionedembodiments, the present invention may be similarly applied to anantenna port.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as the minimumunit allowing the base station to transmit different reference signalsin LTE.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

In the foregoing embodiments, the present invention is configured withhardware by way of example, but the invention may also be provided bysoftware in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A terminal apparatus according to the embodiments described above is aterminal apparatus capable of changing a setting of a configurationpattern of subframes forming one frame, the configuration patternincluding a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the terminal apparatus including: a decoding section thatstores downlink data transmitted from a base station apparatus in abuffer for retransmission and decodes the downlink data; and atransmitting section that transmits a response signal generated using anerror detection result of the downlink data, in which the buffer isdivided into a plurality of regions for each retransmission processbased on a maximum value among numbers of retransmission processesrespectively defined in a plurality of the configuration patternscapable of being set in the terminal apparatus.

In the terminal apparatus according to the embodiments, eachretransmission process in a first configuration pattern is assigned toeach region of a first region group corresponding to a number of firstretransmission processes defined in the first configuration pattern setin the terminal apparatus at a current point in time among the pluralityof regions.

In the terminal apparatus according to the embodiments, when the numberof the first retransmission processes is smaller than the number of theplurality of regions, one of retransmission processes in the firstconfiguration pattern is assigned to a remaining second region groupother than the first region group among the plurality of regions.

In the terminal apparatus according to the embodiments, a number ofretransmission processes corresponding to a difference between thenumber of the plurality of regions and the number of the firstretransmission processes are assigned to each region of the secondregion group.

In the terminal apparatus according to the embodiments, the entiresecond region group is re-divided into a number of regions correspondingto the number of first retransmission processes and all retransmissionprocesses in the first configuration pattern are assigned to therespective re-divided regions.

In the terminal apparatus according to the embodiments, only oneretransmission process in the first configuration pattern is assigned tothe second region group.

In the terminal apparatus according to the embodiments, when the numberof the first retransmission processes is smaller than the number of theplurality of regions, retransmission processes assigned to a region inthe second region group among retransmission processes in a secondconfiguration pattern set last in the terminal apparatus arecontinuously assigned to a remaining second region group other than thefirst region group among the plurality of regions.

In the terminal apparatus according to the embodiments, only oneretransmission process in the second configuration pattern is assignedto the second region group.

In the terminal apparatus according to the embodiments: retransmissionprocesses corresponding to the number of retransmission processesdefined in each configuration pattern are respectively assigned numbersin ascending order from an identical first number in each of theplurality of configuration patterns; a number of retransmissionprocesses corresponding to a minimum value up to a second number inascending order from the first number are fixedly associated with eachregion of a third region group corresponding to the minimum value amonga number of retransmission processes respectively defined in theplurality of configuration patterns among the plurality of regions; anda number of retransmission processes corresponding to a differencebetween the number of the plurality of regions and the minimum value,and a number of retransmission processes corresponding to the differencein retransmission processes from the first number to the second numberare respectively fixedly associated with each region of a remainingfourth region group other than the third region group among theplurality of regions in ascending order from a third number next to thesecond number.

In the terminal apparatus according to the embodiments, the number ofthe plurality of regions is a smaller one of the maximum value and apredetermined threshold.

A buffer dividing method according to the embodiments is a method for aterminal apparatus capable of changing a setting of a configurationpattern of subframes forming one frame, the configuration patternincluding a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the buffer dividing method including: storing downlinkdata transmitted from a base station apparatus in a buffer forretransmission; decoding the downlink data; and transmitting a responsesignal generated using an error detection result of the downlink data,in which the buffer is divided into a plurality of regions for eachretransmission process based on a maximum value among numbers ofretransmission processes respectively defined in a plurality of theconfiguration patterns capable of being set in the terminal apparatus.

The disclosure of the specification, drawings and abstract in JapanesePatent Application No. 2012-159759 filed on Jul. 18, 2012 isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in mobile communicationsystems, for example.

REFERENCE SIGNS LIST

-   -   100 Base station    -   200 Terminal    -   101, 208 Control section    -   102 Control information generating section    -   103, 105 Coding section    -   104, 107 Modulation section    -   106 Data transmission controlling section    -   108 Mapping section    -   109, 218 IFFT section    -   110, 219 CP adding section    -   111, 222 Radio transmitting section    -   112, 201 Radio receiving section    -   113, 202 CP removing section    -   114 PUCCH extracting section    -   115 Despreading section    -   116 Sequence controlling section    -   117 Correlation processing section    -   118 A/N determining section    -   119 Bundled A/N despreading section    -   120 IDFT section    -   121 Bundled A/N determining section    -   122 Retransmission control signal generating section    -   203 FFT section    -   204 Extraction section    -   205, 209 Demodulation section    -   206, 210 Decoding section    -   207 Determination section    -   211 CRC section    -   212 Response signal generating section    -   213 Coding and modulation section    -   214 Primary-spreading section    -   215 Secondary-spreading section    -   216 DFT section    -   217 Spreading section    -   220 Time multiplexing section    -   221 Selection section

1. A terminal apparatus comprising: a receiver, which, in operation,receives, from a higher layer, information indicating an UL/DLconfiguration, which is usable for downlink HARQ and variable pursuantto enhancement for UL-DL Interference Management and Traffic Adaptation(eIMTA), out of a plurality of UL/DL configurations that respectivelydefine composition of uplink subframes and downlink subframes in aframe; and circuitry, which is coupled to the receiver and which, inoperation, stores a received data in a soft buffer having a soft buffersize for a transport block, wherein the soft buffer size is calculatedbased on a same value regardless of variation of the usable UL/DLconfiguration.
 2. The terminal apparatus according to claim 1, whereinthe receiver, in operation, receives the information transmittedaccording to Radio Resource Control (RRC).
 3. The terminal apparatusaccording to claim 1, wherein the soft buffer size is calculated basedon the same value regardless of a maximum number of downlink HARQprocesses allowed for the usable UL/DL configuration.
 4. The terminalapparatus according to claim 3, wherein the maximum number of downlinkHARQ processes allowed for the usable UL/DL configuration is a greatestnumber among multiple maximum numbers of downlink HARQ processesrespectively allowed for multiple usable UL/DL configurations.
 5. Theterminal apparatus according to claim 1, wherein the receiver, inoperation, receives the information that indicates one of multiple UL/DLconfigurations usable for downlink HARQ.
 6. The terminal apparatusaccording to claim 1, wherein the soft buffer size for the transportblock is calculated to be the same regardless of variation of the usableUL/DL configuration.
 7. The terminal apparatus according to claim 1,wherein the usable UL/DL configuration is the same within a cell.
 8. Theterminal apparatus according to claim 1, wherein the same value is
 8. 9.The terminal apparatus according to claim 1, wherein the plurality ofUL/DL configurations consist of 7 UL/DL configurations, of which 3 UL/DLconfigurations are usable for downlink HARQ.
 10. The terminal apparatusaccording to claim 1, wherein the terminal apparatus's total soft buffercapacity is divided into multiple portions each having the soft buffersize for the transport block.
 11. The terminal apparatus according toclaim 1, wherein the circuitry, in operation, decodes the received databy combining the received data stored in the soft buffer with a receiveddata that is retransmitted.
 12. The terminal apparatus according toclaim 1, wherein the soft buffer size for the transport block iscalculated by: obtaining a product of a number of component carrierssupported by the terminal apparatus, a number of layers supported by theterminal apparatus, and the same value; obtaining a ratio between atotal size of the soft buffer and the product; and if the ratio is notan integer, rounding the ratio down to a previous integer.
 13. Acommunication method comprising: receiving, from a higher layer,information indicating an UL/DL configuration, which is usable fordownlink HARQ and variable pursuant to enhancement for UL-DLInterference Management and Traffic Adaptation (eIMTA), out of aplurality of UL/DL configurations that respectively define compositionof uplink subframes and downlink subframes in a frame; and storing areceived data in a soft buffer having a soft buffer size for a transportblock, wherein the soft buffer size is calculated based on a same valueregardless of variation of the usable UL/DL configuration.